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Dispatch queue and pending fetches crash fixes #79

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Dispatch queue and pending fetches crash fixes #79

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2c77465
Fix warning about unowned dispatch queue used to retrieve tile images.
avi-c Apr 17, 2019
e55e4ac
More pendingFetches fixes.
avi-c Apr 17, 2019
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30 changes: 21 additions & 9 deletions MapboxSceneKit/MapboxImageAPI.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -113,7 +113,10 @@ public final class MapboxImageAPI: NSObject {

let group = DispatchGroup()
let groupID = UUID()
pendingFetches[groupID] = [UUID]()
self.pendingFetchesDispatchQueue.sync(flags: .barrier) { [weak self] in
guard let self = self else { return }
self.pendingFetches[groupID] = [UUID]()
}

var completed: Int = 0
let total = bounding.xs.count * bounding.ys.count
Expand Down Expand Up @@ -196,7 +199,10 @@ public final class MapboxImageAPI: NSObject {

let group = DispatchGroup()
let groupID = UUID()
pendingFetches[groupID] = [UUID]()
pendingFetchesDispatchQueue.sync(flags: .barrier) { [weak self] in
guard let self = self else { return }
self.pendingFetches[groupID] = [UUID]()
}

var completed: Int = 0
let total = bounding.xs.count * bounding.ys.count
Expand Down Expand Up @@ -236,7 +242,10 @@ public final class MapboxImageAPI: NSObject {
}

group.notify(queue: DispatchQueue.main) {
self.pendingFetches.removeValue(forKey: groupID)
self.pendingFetchesDispatchQueue.sync(flags: .barrier) { [weak self] in
guard let self = self else { return }
self.pendingFetches.removeValue(forKey: groupID)
}
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@psahgal psahgal Apr 17, 2019 •
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I'm not too familiar with how sync() and group.notify() work, but is it possible this could cause some sort of deadlock on the main queue? From the docs on DispatchQueue:

Attempting to synchronously execute a work item on the main queue results in deadlock.

(I used a slightly different approach for wrapping this call in #80.)

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@avi-c avi-c Apr 17, 2019

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I'm not sure either. I'll take a look at your change. It might be the way to go.

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@psahgal psahgal Apr 17, 2019

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I closed the pull request already, but feel free to reopen it.

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@camdeardorff camdeardorff May 24, 2019

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I cannot speak into the possibility of deadlock here but this is working great for me

completion(error == nil ? imageBuilder.makeImage() : nil, error?.toNSError())
}

Expand All @@ -248,13 +257,16 @@ public final class MapboxImageAPI: NSObject {
**/
@objc
func cancelRequestWithID(_ groupID: UUID) {
guard let tasks = pendingFetches[groupID] else {
return
}
for task in tasks {
httpAPI.cancelRequestWithID(task)
self.pendingFetchesDispatchQueue.sync(flags: .barrier) { [weak self] in
guard let tasks = pendingFetches[groupID] else {
return
}
for task in tasks {
httpAPI.cancelRequestWithID(task)
}

self?.pendingFetches.removeValue(forKey: groupID)
}
pendingFetches.removeValue(forKey: groupID)
}

//MARK: - Helpers
Expand Down
3 changes: 2 additions & 1 deletion MapboxSceneKit/Tile Fetching/MapboxHTTPAPI.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -26,9 +26,10 @@ enum FetchError: Int {
}

internal final class MapboxHTTPAPI {
private static var tileDownloadTaskDispatchQueue = DispatchQueue(label: "com.mapbox.scenekit.api", attributes: [.concurrent])
private static var operationQueue: OperationQueue = {
var operationQueue = OperationQueue()
operationQueue.underlyingQueue = DispatchQueue(label: "com.mapbox.scenekit.api", attributes: [.concurrent])
operationQueue.underlyingQueue = tileDownloadTaskDispatchQueue
operationQueue.name = "Mapbox API Queue"
operationQueue.maxConcurrentOperationCount = 10
return operationQueue
Expand Down